The invention is directed to the field of electronic devices and components, and, more particularly, to a transceiver module including an optical transmitter and an optical receiver.
Optical transmitters and receivers are widely used in communications applications, such as for Local Area Networks (LAN), for example. An optical transmitter typically produces either analog or digital optical signals based upon input electrical signals. Similarly, an optical receiver receives optical signals and produces output electrical signals. The optical signals are often carried by a fiber optic cable which guides the optical signals at a relatively low loss. Moreover, optical signals carried over fiber cables are relatively immune to electrical noise sources as may affect other types of communications via copper wires, for example. Another advantage of optical fiber communication is that information signals having relatively high bandwidths can be carried.
For many applications, such as for a LAN, two-way communications are desirable. Accordingly, an optical transmitter and receiver may be paired within a housing and thereby defining a so-called optical transceiver module. Moreover, since a relatively large number of such two-way links may need to be established, an optical transceiver module may desirably be relatively small so that a high xe2x80x9cport densityxe2x80x9d can be achieved in an apparatus employing a large number of transceiver modules. In other words, a large number of optical transceivers may be collocated within a common housing and connected to common circuitry, such as at a distribution point for an optical LAN.
U.S. Pat. No. 5,604,831 to Dittman et al. discloses an optical transceiver module including a pair of side-by-side circuit board portions, for respective transmitter and receiver devices, and enclosed within an overall housing. Connector pins extend outwardly from the plane of the circuit boards. Along these lines, U.S. Pat. No. 5,047,835 to Corradetti et al. discloses an optical transceiver module including a pair of side-by-side connectors, and their horizontally positioned associated circuit boards within an overall housing. The housing includes a transversely extending wall for mounting the optical devices. U.S. Pat. No. 5,109,454 to Okuno et al. discloses another optical transceiver module with side-by-side circuit boards mounted horizontally and separated by a plastic housing portion.
Unfortunately, as the speed or operating frequencies of the transmitter and receiver are increased, electromagnetic interference (EMI) may be coupled between these circuit portions. The EMI or noise difficulties may become more severe as the sizes of the circuit boards and components are reduced in an effort to increase port density. U.S. Pat. No. 5,047,835 to Chang discloses an overall EMI shield and heat sink which covers the circuit board which, in turn, mounts both the transmitter and receiver circuitry. U.S. Pat. No. 5,117,476 to Yingst et al. discloses an optical transceiver including a common horizontally extending circuit board with individual shields over the transmitter and receiver circuit portions.
Unfortunately, conventional optical transceiver modules are relatively large, especially in terms of their widths, and therefore, the port density may be too low for many useful commercial applications. Moreover, EMI may still be a problem for an optical transceiver, especially as sizes are reduced and higher operating frequencies are used.
In view of the foregoing background, it is therefore an object of the present invention to provide an optical transceiver module which is relatively compact to thereby provide increased port density when combined with other modules.
It is another object of the present invention to provide an optical transceiver module and associated method having enhanced resistance to internally generated EMI.
These and other objects, features and advantages in accordance with the present invention are provided by an optical transceiver module comprising a transmitter portion and receiver portion positioned within a housing with an EMI shield therebetween, and wherein the transmitter and receiver portions comprise respective substrates with opposing spaced apart major surfaces. Considered in somewhat different terms, the substrates are turned on their sides into a vertical orientation with the vertical shield positioned between the substrates within the housing. Accordingly, the port density when using a plurality of such modules is increased, while providing enhanced EMI shielding.
The first and second substrates preferably comprise respective first and second circuit boards. In addition, each substrate may preferably further include a ground plane. The ground planes may be provided by respective conductive layers carried on the second major surfaces or outside surfaces of the substrates. The ground planes and the EMI shield serve to sandwich the active components.
Each circuit board may carry a plurality of generally L-shaped conductive leads extending outwardly for connection to a mounting circuit board, for example. The optical transmitter and optical receiver portions each preferably further comprise at least one active component mounted on the first major surfaces. Accordingly, these active components face one another as positioned in the housing.
According to another advantageous aspect of the present invention, the optical transmitter portion preferably further comprises an optical emitter carried by an end of the first circuit board. The optical receiver portion preferably further comprises an optical detector carried by an end of the second circuit board. In addition, the housing preferably includes an integrally formed transverse bulkhead with respective openings receiving the optical emitter and the optical detector. The transverse bulkhead also defines a forward cavity for receiving an optical fiber connector.
The housing may have a generally rectangular elongate shape and have a series of longitudinally extending slots therein. The EMI shield, and the first and second substrates or circuit boards may be received in respective pairs of slots for convenience of assembly. The EMI shield and the housing preferably comprise an electrically conductive material. The housing may comprise a forward portion and a rearward portion also to facilitate assembly. The housing also preferably further comprises a plurality of keyed mounting projections extending outwardly from a predetermined surface to facilitate mounting. Of course, a plurality of such transceiver modules may be assembled in side-by-side relation on the mounting circuit board to thereby provide a high port density for the apparatus.
A method aspect of the invention is for making an optical transceiver module of a type comprising a housing, an optical transmitter portion comprising a first substrate having a first major surface, and an optical receiver portion comprising a second substrate having a first major surface. The method preferably comprises the steps of positioning the first and second substrates within the housing so that the respective first and second major surfaces are opposing and in spaced apart relation from one another, and positioning an EMI shield within the housing and extending between the first and second major surfaces of the first and second substrates.
Another method aspect of the invention is also for making an optical transceiver module and preferably comprises the steps of forming a housing to have a generally rectangular elongate outer portion, and an integrally formed transverse bulkhead having first and second openings therein and defining a forward cavity for receiving an optical fiber connector therein; and, positioning an optical transmitter portion within the housing comprising a first substrate and an optical emitter carried by an end of the first substrate in registration with the first opening in the bulkhead. The method also preferably further includes the step of positioning an optical receiver portion within the housing comprising a second substrate and an optical detector carried by an end of the second substrate aligned in registration with the second opening of the bulkhead. An EMI shield is preferably positioned within the housing and extends between the first and second substrates.